Short circuit protection for VFDs – is recommended branch circuit protection enough?

Many drive manufacturers have removed semiconductor fuses from VFDs and provide protection guidelines per UL standards. There are multiple levels of short circuit testing and protection; and the manufacturer makes that choice. The question is could you get even better? In many cases, there are options to improve short circuit protection beyond that of the manufacturer recommendation.

Type 2 protection is the best, which means that the device in question recovers from the fault with no damage. Type 2 protection is currently not possible for the IGBTs found in VFDs, as there is no technology available to prevent damage to them. In fact, IGBTs have much lower energy withstand rating compared to other power devices and thus are prone to violent failure during fault conditions. According to Cooper Bussmann “the violent rupture of IGBTs can cause additional damage to other components as a result of expelling gases and shrapnel”.

While type 2 protection cannot be achieved, VFD short circuit protection can be improved. High speed fuses greatly reduce let-through as compared to other options, such as class J fuses or circuit breakers. While these fuses cannot prevent the IGBT from failing, than can prevent the IGBT from rupturing. This can be the difference in a drive repair or a full replacement. The savings could be significant, particularly in larger drive frames.

To get started with Short Circuit Protection for VFDs, give us a call at  800.993.3326 or email our motor services team at eecomotorteam@eeco-net.com.